Optical element with an opaque chrome coating having an aperture and method of making same

Abstract

A substrate includes an opaque chrome coating on a surface of the substrate dry-etched to form an aperture, wherein chrome in the aperture is below detectable limit. A method of forming an opaque chrome coating on a substrate includes depositing an initial thickness of the opaque chrome coating on the substrate without ion-assist or with undetectable ion-assist and depositing the remainder of the opaque chrome coating with or without ion-assist. In one embodiment the invention is directed to an apertured optical element having a substrate transmissive to light and an opaque chrome coating on the substrate defining an aperture. Three- and four-layer opaque coatings of various materials are disclosed, including three-layer chrome/chrome oxide/chrome coatings.

1. An article comprising:
 a substrate; 
 an opaque chrome coating having an optical density greater than or equal to 3 formed on a surface of the substrate and etched to form an aperture within the coating, 
 wherein chrome in the aperture is below detectable limit and the edge of the chrome coating defining the circumference of the aperture is sloped at an acute angle in a range from 10° to less than 15°. 
 
     
     
       2. The article of  claim 1 , wherein the opaque chrome coating comprises a first layer comprising chrome, a second layer comprising chrome oxide, and a third layer comprising chrome. 
     
     
       3. The article of  claim 2 , wherein a thickness of the first layer is less than 10 nm and the chrome content of the first layer is greater than 50%. 
     
     
       4. The article of  claim 2 , wherein a thickness of the second layer is in a range from approximately 30 to 52 nm and an oxygen content of the second layer is in a range from 35 to 60 at. %. 
     
     
       5. The article of  claim 3 , wherein a thickness of the third layer is at least 90 nm and a chrome content of the third layer is greater than approximately 80 at. %. 
     
     
       6. The article according to  claim 4  wherein said third layer is a densified layer produced during deposition by use of ion-beam assistance. 
     
     
       7. The article according to  claim 1 , wherein the opaque chrome coating has an optical density greater or equal to 3.8. 
     
     
       8. The article according to  claim 1 , wherein the opaque chrome coating first layer is 4-6 nm thick, the second layer is approximately 40-45 nm thick and the third layer is 100-110 nm thick. 
     
     
       9. The article according to  claim 2 , wherein the third layer is a densified layer, the densification resulting from the use of ion-beam assistance during application of the third layer, the ion-beam having an ion energy in the range of 50-600 V and a current density in the range of 0.17-0.4 mA/cm 2 . 
     
     
       10. The article according to  claim 2 , wherein said coating further comprises a fourth layer, said fourth layer being chrome oxide, and said coating is etched to form an aperture within said coating, and said fourth layer is a densified layer, the densification resulting from the use of ion-beam assistance during application of the third layer, the ion-beam having an ion energy in the range of 50-600 V and a current density in the range of 0.17-0.4 mA/cm 2 . 
     
     
       11. A window comprising:
 an opaque chrome coating dry-etched to form an aperture within the coating, the opaque chrome coating having an optical density greater than or equal to 3, 
 wherein chrome in the aperture is below detectable limit and the edge of the chrome layer defining the circumference of the aperture is sloped at an acute angle in a range from 10° to less than 15°. 
 
     
     
       12. The window of  claim 11 , wherein the opaque chrome coating comprises a first layer comprising chrome, a second layer comprising chrome oxide, and a third layer comprising chrome. 
     
     
       13. The window of  claim 11 , wherein a thickness of the first layer is less than 10 nm and the chrome content of the first layer is greater than 50 at. %. 
     
     
       14. The window of  claim 11 , wherein a thickness of the second layer is in a range from approximately 30 to 52 nm and an oxygen content of the second layer is in a range from 35 to 60 at. %. 
     
     
       15. The window of  claim 12 , wherein a thickness of the third layer is at least 90 nm and a chrome content of the third layer is greater than approximately 80 at. %. 
     
     
       16. The window according to  claim 13  wherein said third layer is a densified layer produced during deposition by use of ion-beam assistance. 
     
     
       17. The window according to  claim 11 , wherein the opaque chrome coating has an optical density greater or equal to 3.8. 
     
     
       18. The window according to  claim 12 , wherein the opaque chrome coating first layer is approximately 4-6 nm thick, the second layer is approximately 40-45 nm thick and the third layer is approximately 100-110 nm thick. 
     
     
       19. The window according to  claim 12 , wherein the third layer is a densified layer, the densification resulting from the use of ion-beam assistance during application of the third layer, the ion-beam having an ion energy in the range of 50-600 V and a current density in the range of 0.17-0.4 mA/cm 2 .